There has been conventionally known a structure in which a spacer is held between unit cells in a battery assembly so as to form a cooling passage, through which a cooling medium passes, so that the cooling medium passing the cooling passage cools the unit cells that generate heat by repeated electric charging/discharging.
JP 2006-073461 A (paragraphs 0025 to 0027 and FIG. 2) discloses a spacer held between battery modules. In the spacer, first abutting portions that abut against a first battery module out of two adjacent battery modules and second abutting portions that abut against a second battery module are alternately disposed, and thus, cooling passages in which the first battery module is brought into contact with a cooling medium and other cooling passages in which the second battery module is brought into contact with the cooling medium are alternately formed. Moreover, the spacer is provided with walls for preventing the cooling passages from being narrowed when the battery modules expand between the first abutting portion and the second abutting portion.
JP 2004-031364 A (paragraph 0056 and FIG. 5) discloses a corrugated spacer held between battery modules, wherein cooling passages are defined by clearances between the spacer and the battery modules.
JP 2004-047426 A (paragraphs 0035 to 0041 and FIG. 7) discloses disposing a spacer having cooling passages formed thereat between secondary batteries and interposing a corrugated plate between the secondary batteries. In particular, JP 2004-047426 A discloses a spacer in which structures, each having a lateral bar and a vertical wall combined with each other, define two kinds of cooling passages alternately arranged.
JP 2010-140802 A (paragraphs 0028 and 0029 and FIG. 2) discloses a cell holder (i.e., a spacer) in which recesses and projections linearly extending at a surface opposite to a storage cell are alternately arranged, wherein a cooling passage is defined in a clearance defined between the recess and the storage cell.
JP 2010-186681 A (paragraphs 0017 and 0018 and FIG. 2) discloses a battery holder (i.e., a spacer) in which grooves are formed at both surfaces of a base wall, and then, a cooling passage is formed from a slit at a support frame at one end of the base wall to a slit at a support frame at the other end through the grooves.
JP 2010-015949 A (paragraph 0022) discloses an uneven spacer having projections and grooves alternately arranged, wherein a cooling medium is allowed to pass through the grooves.
These spacers described in the prior art documents are all prone to elongate in a direction perpendicular to the cooling passages because of their corrugated shapes, because of which, when the adjacent unit cells expand, the distance between the adjacent unit cells is reduced. Such reduction in the distance between adjacent unit cells reduces the flow path cross-sectional area of the cooling passages, whereby the cooling efficiency is decreased.